iOS Swift runtime实现方法交换

//
//  ViewController.swift
//  SwiftApp
//
//  Created by 彭思 on 2020/11/23.
// Swift Runtime方法替换

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        print("这是一个方法:viewDidAppear")
    }
}

extension UIViewController {
    public class func initializeMethod(){
        let originalSelector = #selector(UIViewController.viewDidAppear(_:))
        let swizzledSelector = #selector(UIViewController.myMethod(animated:))

        let originalMethod = class_getInstanceMethod(self, originalSelector)
        let swizzledMethod = class_getInstanceMethod(self, swizzledSelector)

        //在进行 Swizzling 的时候,需要用 class_addMethod 先进行判断一下原有类中是否有要替换方法的实现
        let didAddMethod: Bool = class_addMethod(self, originalSelector, method_getImplementation(swizzledMethod!), method_getTypeEncoding(swizzledMethod!))
        //如果 class_addMethod 返回 yes,说明当前类中没有要替换方法的实现,所以需要在父类中查找,这时候就用到 method_getImplemetation 去获取 class_getInstanceMethod 里面的方法实现,然后再进行 class_replaceMethod 来实现 Swizzing
        if didAddMethod {
            class_replaceMethod(self, swizzledSelector, method_getImplementation(originalMethod!), method_getTypeEncoding(originalMethod!))
        } else {
            method_exchangeImplementations(originalMethod!, swizzledMethod!)
        }
    }

    @objc func myMethod(animated: Bool) {
        self.myMethod(animated: animated)
        print("替换了")
        self.view.backgroundColor = UIColor.yellow
    }
}

调用：

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    // Override point for customization after application launch.
    UIViewController.initializeMethod()
    return true
}